Marestail Woes
Driving around the country side this season, it’s very clear that marestail (horseweed) issues in soybeans are abundant. Although waterhemp is still a big problem, there are also a lot of marestail plants. Like waterhemp, fields need to be aggressively managed for marestail.
The first step in successfully controlling any weed is to understand it’s biology. Marestail can follow either a winter or summer annual life cycle but the majority will emerge in the fall. Unlike other winter annuals, marestail doesn’t fully mature until late summer. This cycle puts marestail in much greater competition with soybeans than other winter annuals. The plants generally flower in July, seed and then disperse from August to October (right now!). Each plant can produce up to 200,000 seeds. Like other weeds, marestail is dispersed through wind, animals, and even your combine. Up to 90% of plants that emerge in the fall can survive the winter, leaving you with a bigger control issue in next year’s crop.
So, what can you do now to prepare your fields for next season?
1. Fall Burndown
The majority of marestail emerges in the fall; this is your BEST opportunity to manage it. A word of caution, a burndown without residual, only kills plants that are emerged, leaving opportunity for more plants to emerge unscathed. Seriously consider a residual addition to your burndown application.
2. Tillage
If you are in a no-till situation, this may help a little bit but do not rely on this to relieve all your weed pressure. In fact, we had a conversation with a chemical rep who discussed the issues of minimal tillage equipment only goose-necking the plants. This doesn’t actually kill the plants and can cause herbicide take-up issues later on.
3. Spring Burndown
At least 1-2 weeks prior to planting your soybeans, apply a spring burndown that includes a strong dose of 2,4-D and a residual herbicide. Marestail is best controlled while still in the rosette stage or less than 2 inches tall.
4. Plant Traited Beans
Conventional beans have by far the heaviest marestail populations. If you cannot get a handle on weed control, this is a great opportunity for you to make the switch to a traited bean. This will greatly increase your herbicide options for control. A premium on conventional beans doesn’t mean a lot if you spend more money on additional herbicide applications that only *maybe* control the weeds.
5. Don’t Skip on Two-pass
Plan on a two-pass, strong residual program for long-term effectiveness of controlling weeds. Never let weeds get above 4-6 inches tall to maximize herbicide effectiveness. This means you need to be out scouting all season long.
6. Contact your Agronomist
Marestail is not a weed to take lightly. Like waterhemp, it can do serious yield damage and can remain an issue for years to come. Our goal is to find the best solution to maximize your operation’s effeciency.